How many times did you cycle it? As in , full charge to 0, then recharge. It took my battery in my m5500 a couple cycles to get to it's potential, which ended up at about 2.5hours
ALso, there are setting in both bios, and under battery properties (these are accessible by rt clicking on the battery icon on your toolbar/desktop).
The bios battery option should be set to power saving or something similar
You can set the battery properties to max battery to preserve its lifespan as well.
Other things will vary life as well, such as the apps you are running, screen brightness etc. But, after all I mentioned, with the Sentia you should get minimal of 3 hours.
Though, it does depend on the processor you have, the faster ones use more power, regardless of the fact that it is an M series.
Hope this helps